Abstract
ERp57 is a ubiquitous ER chaperone that has disulfide isomerase activity. Here, we found that both ERp57 and gastric H+,K+-ATPase are expressed in a sample derived from the apical canalicular membranes of parietal cells. Overexpression of ERp57 in HEK293 cells stably expressing H+,K+-ATPase significantly increased the ATPase activity without changing the expression level of H+,K+-ATPase. Interestingly, overexpression of a catalytically inactive mutant of ERp57 (C57S/C60S/C406S/C409S) in the cells also increased H+,K+-ATPase activity. In contrast, knockdown of endogenous ERp57 in H+,K+-ATPase-expressing cells significantly decreased ATPase activity without changing the expression level of H+,K+-ATPase. Overexpression and knockdown of ERp57 had no significant effect on the expression and function of Na+,K+-ATPase. These results suggest that ERp57 positively regulates H+,K+-ATPase activity apart from its chaperoning function.
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